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Ventilation, another question

Posted: Tue Jan 28, 2014 9:06 am
by IglooDamus
I just got my Icebox, and a friend and I built an 8 footer in the back yard. Had some issues with the build but I think I understand a lot better now, that's not why I'm writing. Last night I tried to sleep in it, it was about -20 F here so I was curious to see if a couple candles could really keep me warm. For ventilation, I poked a ~1" hole (though maybe it was slightly smaller, at least 3/4") at the top of the igloo, as close to the center as I could manage. I used the inner panel of the Icebox form as the door, with a towel draped over the top to block the gap between the form and the igloo. I had three candles going and temperature-wise I was totally comfortable. I think the temperature was pretty close to freezing - I didn't have a thermometer, but I had two jars of water, one that had started to ice up and one that was all liquid, and after 2+ hours, the liquid was still liquid, and the ice content in the other had stayed about the same. So I guess it can't have been much above or much below freezing.
Anyway, after sleeping for about two hours, I woke up feeling quite disoriented and a bit nauseous with a bit of a headache, I am almost certain it was because the oxygen level had dropped in the igloo. I could be wrong, because the candles were still burning with no problem, but as soon as I left the igloo I started to feel much better.

So what did I do wrong? I have seen a couple references to "carbon dioxide traps" which occur I guess when the only ventilation besides the hole on top is below the level of the sleeping shelf? But that doesn't seem right, as the manual suggests having the top of the door below the sleeping shelf. Should I not have had candles going for so long? Before trying to sleep, I had the candles out there for about 3 hours, and for an hour of that I was out there with my friend. Or is it just the quantity? Is three candles too many? I was so comfy temperature-wise, I could've definitely done with fewer candles, but I don't know how quickly the igloo would cool down if I put out all three.

Anyway, any tips would be very appreciated.

Re: Ventilation, another question

Posted: Tue Jan 28, 2014 4:30 pm
by Banff Martin
Hello IglooDamus,

Finally, another poster on the forum this season other than just Ed & myself! :)

First, I've read here that the ideal location for the air hole is above the door & high up the wall, but not at the 'top' of the igloo. An advantage of this is that it prevents much cross-draft of the cold air movement over the occupants.

The primary reason for the floor to be above the top of the door is thermal; with drafts reduced, colder air cannot displace the warmer air above it. This makes the entranceway a cold trap. I suppose it does make sense that the CO2 should also sink down there as well.

I'm sure your condition was caused by low O2 in the igloo. This doesn't mean that there was an accumulation of CO2, just less O2 than normal. I haven't seen it myself, but I've read that the candle flames will reach up higher when this occurs and should be watched for as a warning sign.

I suggest widening your air hole to 1", and reducing the air-tighted-ness of the entranceway. The objective is to dampen drafts (ideally with a double hanging material, one on the outside, one on the inside) but not to seal it. I expect that leaving a crack or two in the 'plugging' plus slight widening of the air hole should solve your issue.

When I've slept in my igloos I put out the candles, but that's because I prefer to sleep in the dark and had solid gear - I wasn't concerned with the igloo temperature. I've lounged in mine with 4 candles going one without issue. With a couple people I would only have a candle going for light; we put off lots or warmth.

Welcome to igloos!

Re: Ventilation, another question

Posted: Wed Jan 29, 2014 8:13 am
by IglooDamus
Thanks for your reply!

That is interesting about the candle flames, I just assumed that the effect would be the opposite. It could well be that the candles were reaching higher, but I wasn't looking for that and easily could have missed it.
I should have put out the candles but it was damn cold and I was nervous my first night out. Plus my bag and liner are only rated to 6-10 F, and I think that means you can survive at those temperatures, not sleep comfortably. Definitely, it would have been nicer to sleep without all that light (it is impressive how much light a candle gives off in an igloo, with all those reflections).
Anyway, I'll try again tonight. Temperatures are supposed to be up about 30-35 degrees from last time, so I should be able to sleep fine without the candles.

Thanks again for your thoughts, I can't wait to get out and build an igloo for real ... i.e. not in my backyard.

Re: Ventilation, another question

Posted: Wed Jan 29, 2014 10:17 am
by Banff Martin
Yes, it is a logistical challenge to find a build site that is legal for camping and that also works for you..! For the first couple times though, building near home is quite reassuring, and the bathroom is warm! =)

For improving your warmth I'd suggest a few things:
- I'd seal the original air hole with snow from within & outside, and drill a new one that is high up the wall but directly above the entrance. This should reduce cold air hitting you.
- You didn't detail your gear other than your sleeping bag & liner; what kind of pad are you using under your sleeping bag? I use a pair of Therma-rests under mine for insulation. Some manner of pad is mandatory.
- I like to wear lightweight water-wicking thermal underwear & wool socks. If you get too warm you'll stay dry & comfortable. Igloos can be humid, so I prefer some manner of moisture management. Finding a hat that does this well can be a challenge.
- To improve on your light sleeping bag you may want to lightly drape a heat-reflective mylar blanket over top of you. Make sure it is loose though, as it doesn't breathe and can cause moisture to accumulate within your bedding.
- A pair of 8-hour heat packs within your bag might count as cheating, but you don't have to admit to it. =)

And for us men...a rinsed 2L milk jug with cap can prevent that chilling midnight run outside to the bathroom. ;)

For when you're not in the sleeping bag I insist on some kind of barrier between myself & the floor. I find mylar-coated bubble wrap quite effective - you can buy it at hardware stores and cut it into multiple 'seats'; it comes in a roll. Otherwise even with ski pants I eventually get cold or wet.

If you build a 9' model you'll have enough space to cut in a short entrance, leave 6-8" of snow, then cut out a cube of snow closer to the center of the igloo, and sit with your legs in the 'cube'; the airspace is segregated and should be closer to freezing vs. the outside temperature.

Have fun!

Candles, Sleeping Pads (was: Ventilation, another question0

Posted: Tue Feb 04, 2014 6:22 pm
by wrjdrk
Hi all,

I noticed the mention of candles and have a question about the best place to put them.

It seems that the ideal spot for a candle in an otherwise occupied igloo would be on the floor directly below the ventilation hole in the roof -- but that would happen to be right in the way of any human activities. I've tried putting a candle in a little alclove to the side, but the heat ends up melting a long trough above it. I would tend to be leary of hanging a candle (or a candle lantern) anywhere above sleeping gear, because the hot draft from the candle would tend to dislodge whatever it is hanging from. So, where do you put candles?

My other question is, what to do about the sliperiness of multiple layers of insulated padding materials underneath one's sleeping bag -- how do you keep all that stuff put and not have it squeeze out from under you?

Friendly greetings to all,


Re: Ventilation, another question

Posted: Wed Feb 05, 2014 10:53 am
by Banff Martin
Hello Debbie,

When I've used candles I've put them as close to the trench edge as I could to get away from the wall, while at the same time keeping them away from areas of use. I place a couple on a piece of wood to give a stable surface. If you wanted to hang something I'd suggest drilling a hole in the pad and putting a rod into that, with attachments to it such as a horizontal piece; a pair of vertical rods could allow a stable horizontal rod above the trench? I haven't tried this but perhaps it would work. Whatever touches the igloo walls or floor can't be metal of course, as it would conduct any heat. You may find other ideas at ... f=20&t=207, the 'Furnishing and customizing igloo interiors' thread.

Good question! I haven't really looked at this and it would depend on the gear you have. My first thought is using extra-long shoelaces or twine banded around layers to keep them together. Perhaps two would do, horizontally around the 1st & 2nd thirds of the bedding? Picturing a sleeping bag being bound like this is a funny picture and may not work so well; perhaps there are loops on the bag that could be tethered to the bound bedding?

Re: Ventilation, another question

Posted: Thu Feb 06, 2014 2:12 pm
by Banff Martin
Debbie, upon discussing this with a Cub Scout leader a simple method is to layer non-slippery material between others, such as a wool blanket.

At the same time she warns that tying layers together that contain air may result in creating cold spots if done too tightly.

Re: Ventilation, another question

Posted: Sun Mar 02, 2014 8:22 pm
by Igloo Ed
The natural convection currents in an igloo are: up in the middle and down along the cold walls. It is best to add heat to the center of this and sit as close to it as possible.
Putting the candles in the trench and between your feet is a luxury.